I. Field
The following description relates generally to wireless communications systems, and more particularly to independent power control of multiple carriers for High-Speed Uplink Packet Access (HSUPA).
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so forth. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems including E-UTRA, and orthogonal frequency division multiple access (OFDMA) systems.
An orthogonal frequency division multiplex (OFDM) communication system effectively partitions the overall system bandwidth into multiple (NF) subcarriers, which may also be referred to as frequency sub-channels, tones, or frequency bins. For an OFDM system, the data to be transmitted (i.e., the information bits) is first encoded with a particular coding scheme to generate coded bits, and the coded bits are further grouped into multi-bit symbols that are then mapped to modulation symbols. Each modulation symbol corresponds to a point in a signal constellation defined by a particular modulation scheme (e.g., M-PSK or M-QAM) used for data transmission. At each time interval that may be dependent on the bandwidth of each frequency subcarrier, a modulation symbol may be transmitted on each of the NF frequency subcarrier. Thus, OFDM may be used to combat inter-symbol interference (ISI) caused by frequency selective fading, which is characterized by different amounts of attenuation across the system bandwidth.
Generally, a wireless multiple-access communication system can concurrently support communication for multiple wireless terminals that communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
One issue with wireless systems relates to multicarrier controls for high-speed uplink packet access (HSUPA). In general, HSUPA employs a packet scheduler, but operates on a request-grant principle where user equipment or devices can request permission to send data and a scheduler decides when and how many devices will be allowed to do so. A request for transmission contains data about the state of the transmission buffer and queue at the device and its available power margin. In addition to this scheduled mode of transmission applicable standards also allow a self-initiated transmission mode from the devices, denoted non-scheduled. With respect to transmitted power and multicarrier control however, previous systems were only able to achieve such control via power controls that were universally applied to all carriers. This type of non-independent control over the carriers made it difficult to regulate power among the carriers and control interference between devices and/or channels. Moreover, in addition to non-independent control, multicarrier control systems did not have the capability to properly scale power allocations between carriers when conditions dictated. Such lack of control independence and scaling made it exceedingly difficult to deliver the quality of service desired.